Touch-sensitive display devices allow users to interact with computers using fingers, passive styli, active styli, and other input objects. The touch-sensitive display device may detect a touch event each time an input object touches or comes into close proximity with a touch sensor of the touch-sensitive display device. The touch sensor typically includes a plurality of touch-sensing electrodes distributed across the touch sensor to enable capacitance measurements at specific XY locations. A touch event may therefore be interpreted by the touch-sensitive display device as a user input at a particular two-dimensional location relative to the touch-sensitive display device.
Active styli typically include one or more stylus electrodes. These electrodes can be driven with a particular excitation signal to influence electrical conditions on a touch sensor, and/or they can be configured to detect an excitation signal applied to touch-sensing electrodes of the touch sensor.